Drill bit

ABSTRACT

A drill bit of the present invention is intended to stably perform drilling by lessening a great change in a drilling condition and to avoid reduction of a drilling efficiency even when large chip lumps are generated. In the drill bit, the main cutting blades have main cutting edges each structured such that an inner end thereof is located at the rotation center of the drill and an outer end thereof is located on an outer periphery of a rotation trace of the cutting blades, and the sub cutting blades have sub cutting edges each structured such that an inner end thereof is located to be spaced radially outward apart from the rotation center and an outer end thereof is located to be spaced radially inward apart from the outer periphery of the rotation trace toward the center of rotation.

TECHNICAL FIELD

The present invention relates to a drill bit constructed such that acutting blade body made of cemented carbide is integrally and fixedlyattached to a tip end of a bit body by brazing, welding, or the like.More particularly, the present invention relates to a drill bit that hashigh drilling efficiency in drilling a hole in concrete, stone, etc.

BACKGROUND ART

Drilling (Boring) a hole in concrete, stone, etc, is done by attaching adedicated drill bit to a rotating hammer drill and by applying both anaxial vibrational striking force and a rotational torque to the drillbit. This type of drill bit is constructed such that a cutting bladebody made of wear-resistant cemented carbide is fixedly attached to atip end of a steel bit body by brazing, welding or the like. Inaddition, chip discharge grooves are provided on an outer periphery ofthe bit body so as to correspond to concave portions formed on cuttingblades of the cutting blade body. Further, a standardized shank portionis attached to a base end portion of the bit body and configured to becoupled to a drive shaft of the hammer drill.

The applicant disclosed a novel drill bit of this type (Japanese PatentApplication No. 2000-377082). This drill bit is constructed such that aplurality of cutting blades extend substantially radially outward fromthe center of a block-like cutting blade body fixedly attached to a tipend of a bit body. Each cutting blade has a face and a flank. An edgeformed at a boundary between the face and the flank of the cutting bladeto protrude toward a tip end of the cutting blade body to form a cuttingedge. And, inner ends (ends on the center side) of the cutting bladesare coupled to form the tip end pointed without a chisel edge. Betweenadjacent cutting blades, a chip discharge groove is formed by a concaveportion recessed backward. The chip discharge groove is continuous witha wide bit chip discharge groove provided on an outer periphery of thebit body.

In accordance with the drill bit constructed as described above, duringdrilling the hole in the concrete, the stone, etc, cutting (striking andcutting) is performed in such a manner that the cutting blade impactlystrikes a cutting face of a drill hole, thereby generating chips. Thesechips move up from the cutting face of the drill hole according to anaxial movement of the drill bit, and moves through each chip dischargegroove. Then, the chips are discharged into the wide bit chip dischargegroove. As should be appreciated, the chips are smoothly dischargedoutside the drill hole. Thus, regardless of a depth of the drill hole,the chips are efficiently discharged. Further, since the tip end of thecutting blades is pointed without the chisel edge, the center ofrotation is uniquely determined in drilling, thereby allowing thecutting blades to stably rotate. As a consequence, it is possible toeasily drill a hole having a desired diameter and a desired shape. Inaddition, highly durable drill bit is achieved.

However, in the above-constructed drill bit, the cutting blades of thecutting blade body are configured (structured) in the same manner.Because of this, when the cutting blade strikes hard object such asreinforcing steel within concrete or stone during drilling the hole inthe concrete or the like, an impact force concentratively acts on thecutting blade that has struck the object or its adjacent cutting blade,thereby causing a great change in a drilling condition.

During drilling, various sizes of large and small chips, including largechip lumps, are generated on the cutting face of the drill hole. Sincethe large chip lumps are crushed into small chips during repeatedstriking and cutting, drilling is not impeded by the large chip lumps.However, while the large chip lumps are being struck and crushed by thecutting edge of the drill bit, the cutting edge does not perform acutting action for the cutting face of the drill hole, that is, thecutting action is interrupted. This reduces drilling efficiency.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a drill bit capable ofcarrying out drilling as stably as possible by lessening a great changein a drilling condition and without reducing drilling efficiency whenlarge chip lumps are generated in drilling a hole in concrete, stone,etc.

In order to achieve the above object, a drill bit of the presentinvention comprises a plurality of cutting blades, each of which isprovided at a tip end of a drill and disposed to extend substantiallyradially outward from a rotation center side of the drill and has acutting edge formed by protruding an edge between a face and a flank ofeach cutting blade toward a tip end of the drill; and a shaft-shaped bitbody attached to a base end side of the cutting blades and having a baseend portion coupled to a shank portion, the drill bit being configuredto perform striking and cutting by a combination of a rotation and anaxial movement, wherein the cutting blades include at least two maincutting blades and at least two sub cutting blades each disposed betweenadjacent main cutting blades in a circumferential direction of thecutting blades, the main cutting blades have main cutting edges eachstructured such that an inner end thereof is located at the rotationcenter of the drill bit and an outer end thereof is located on an outerperiphery of a rotation trace of the cutting blades, and the sub cuttingblades have sub cutting edges each structured such that an inner endthereof is located to be spaced radially outward apart from the rotationcenter and an outer end thereof is located to be spaced radially inwardapart from the outer periphery of the rotation trace toward the centerof rotation.

In accordance with the drill bit constructed as described above, indrilling a hole in concrete, stone, etc, cutting of the cutting face ofthe drill hole (involving crushing of chips on the cutting face of thedrill hole) is struck by the main cutting edge extending from therotation center to the outer end of the cutting blade, and the subcutting edge assists in the cutting performed by the main cutting edge.In other words, the sub cutting edge assists in striking and cuttingperformed by the main cutting edge, and they cooperate with each otherto carry out efficient cutting. Since the outer end of the sub cuttingedge is located closer to the rotation center than the outer end of themain cutting edge, and hence the sub cutting edge does not contact theinner surface of the drill hole, efficient striking and cutting areaccomplished by reducing a cutting resistance in the whole drill bit. Inaddition, since the outer periphery of the main cutting edge is guidedby an inner peripheral surface of the drill hole, a hole in a desiredshape (circular hole) can be drilled.

In the drill bit, the main cutting edges of the main cutting blades maybe each inclined so as to retreat on the outer end side, and the innerends of the main cutting edges may be coupled to one another atsubstantially the rotation center to form a tip end of the cuttingblades. Thereby, the tip end of the cutting blades conforms to therotation center, and thus, the cutting blades stably rotate. Inaddition, striking and cutting are performed effectively in such amanner that the tip end of the cutting blades strikes the cutting faceof the drill hole.

In the drill bit, the sub cutting edges of the sub cutting blades may beinclined at an equal angle and in the same direction with respect to themain cutting edges of the main cutting blades. In a manufacturingprocess, each cutting blade is formed to have the face and the flank bycutting, and the main cutting edge and the sub cutting edge are formedby “sharpening” under the same conditions and easily. Consequently, adrill bit can be manufactured with increased productivity.

In the drill bit, the sub cutting edges may be located to retreatrelative to the main cutting edges. In this structure, the main cuttingedges in large part carries out the direct striking and cutting of thecutting face of the drill hole, and the sub cutting edges effectivelycrush large chip lumps generated and sandwiched between the main cuttingedges. In other words, during drilling, the large chip lumps generatedon the cutting face of the drill hole and the concurrent drilling arecarried out effectively by cooperation between adjacent main cuttingedge and sub cutting edge. Consequently, a higher drilling efficiency isgained as compared to the conventional drill bit.

In the drill bit, a crush face may be formed between the sub cuttingedge and the rotation center to retreat relative to the sub cuttingedge. In this structure, the large chip lumps generated by the strikingand cutting performed by the main cutting edge or the like aresandwiched between the main cutting blade and the sub cutting blade andeffectively crushed between the crush face and the cutting face of thedrill hole. Because the large chip lumps are crushed into small chips,the operations of the main cutting edges and the sub cutting edges arenot interrupted by the large chip lumps. So, striking and cuttingcontinue effectively. Consequently, high drilling efficiency is gained.

In the drill bit, the crush face may be inclined downward on the flankside of the sub cutting blade. Thereby, since the large chip lumps arecrushed into small chips by the cutting face as described above and thesmall chips are pushed out from the cutting blade into the chipdischarge groove by the inclination of the cutting face, the chips canbe discharged more efficiently.

In the drill bit, the main cutting blades and the sub cutting blades maybe integral with each other to form a block of a cutting blade body, andthe cutting blade body may be fixedly attached to a tip end of the bitbody. In manufacturing process, the main cutting blades and the subcutting blades are molded in an integral block shape by sintering andcasting, and easily fixedly attached to the tip end of the bit body bywelding or the like. Thus, the cutting blade body can be efficientlymanufactured.

In the drill bit, the main cutting blade and the sub cutting blade maybe alternately disposed in the circumferential direction to extend fromthe tip end of the cutting blades, and may be substantiallyasterisk-shaped such that the cutting blades extend from the tip end asseen in a bottom view. This is desirable since the gap between thecutting blades can be utilized as the chip discharge groove. In thiscase, in the drill bit having an outer diameter of approximately 6 mm to20 mm, about four to eight cutting blades, including the main cuttingblades and the sub cutting blades, are desirably embodied. It ispreferable that even-numbered cutting blades are provided such that themain cutting blade and the sub cutting blade are alternately disposed,and odd-numbered cutting blades are provided such that the main cuttingblade and the sub cutting blade are alternately disposed and the maincutting blade and the main cutting blade are disposed adjacent eachother at one position.

In the drill bit, a concave chip discharge groove may be formed betweenadjacent cutting blades, and a bit chip discharge groove may be formedon an outer peripheral face of the bit body to extend continuously withthe chip discharge groove. Thereby, it is possible to efficientlydischarge the chips generated at the cutting face of the drill holeoutside the drill hole.

In the drill bit, the cutting blades may be formed of cemented carbide,and the bit body may be formed of steel. Thus, it is possible to providea drill bit comprised of the cutting blades made of cemented carbidewith high cutting ability and high wear-resistance and being capable ofexhibiting high performance in a-reduced cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view showing a construction of a drill bit accordingto an embodiment of the present invention;

FIG. 2 is a bottom view showing a structure of a lower end face (bottomface: face used for striking and cutting) of a cutting blade body of thedrill bit;

FIG. 3 is a perspective view of the cutting blade body of the drill bitin FIGS. 1 and 2 as seen from a tip end side of the cutting blade body;and

FIG. 4 is an enlarged bottom view of the cutting blade body forexplaining a rotation trace of cutting blades of the cutting blade body.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an example of an embodiment of the present invention willbe described with reference to the drawings.

As shown in FIG. 1, a block-like cutting blade body 2 made of cementedcarbide shown in FIGS. 1 to 3 is integrally and fixedly attached to atip end of a steel bit body 1 by a known method, for example, weldingsuch as brazing or friction welding with pressure.

In this embodiment, the cutting blade body 2 is provided with sixcutting blades 2 a, 2 b, 2 c, 2 d, 2 e, and 2 f configured to extendsubstantially radially to be equally spaced apart in a circumferentialdirection of the cutting blade body 2, i.e., at intervals of 60 degreessuch that cutting edges extend radially outward from a rotation center(center of rotation) side. Each of the cutting blades 2 a, 2 b, 2 c, 2d, 2 e, and 2 f has a face 3 located forward and a flank 4 locatedrearward in rotation of drilling. Each cutting edge is formed by an edgebetween the face 3 and the flank 4 to extend substantially radially. Theedge is configured to protrude (downward in FIG. 1 and upward in FIG. 3)toward a tip end of the cutting blade body 2. In this embodiment, sixcutting edges are formed to be equally spaced apart from each other inthe circumferential direction so as to correspond to the cutting blades2 a, 2 b, 2 c, 2 d; 2 e, and 2 f. In this embodiment, therefore, the sixcutting edges include three main cutting edges 6 and three sub cuttingedges 7 disposed at intervals of 60 degrees.

In this embodiment, the cutting edges have two types, i.e., the maincutting edges 6 and the sub cutting edges 7. As shown in FIGS. 2 and 4,the main cutting edge 6 and the sub cutting edge 7 are alternatelydisposed at the tip end of the cutting blade body 2 as seen from abottom face of the cutting blade body 2. Also, the cutting blades 2 a, 2c, and 2 e provided with the main cutting edges 6 are main cuttingblades and the cutting blades 2 b, 2 d, and 2 f provided with the subcutting edges 7 are sub cutting blades. Inner ends of the main cuttingedges 6 are located at a tip end 5 which is formed by coupling the innerends of the main cutting edges 6 and serves as the center of rotation.Outer ends 12 of the main cutting edges 6 are located to be spacedradially outward apart from the center of rotation (tip end 5), to beprecise, on an outer periphery (outermost periphery) of a rotation traceof the cutting blade body 2.

Inner ends 7 i of the sub cutting edges 7 are located to be spacedradially outward apart from the tip end 5 which is the center ofrotation. Crush faces 8 are formed between the tip end 5 and the innerends 7 i of the sub cutting edges 7. While the outer ends 12 of the maincutting edges 6 are located on the outer periphery of the cutting bladebody 2, outer ends 11 of the sub cutting edges 7 are located slightlyradially inward relative to the outer periphery of the cutting bladebody 2. More specifically, the length of the cutting blades 2 b, 2 d,and 2 f having the sub cutting edges 7 at tip ends thereof (length fromthe inner ends to the outer ends) is shorter than that of the cuttingblades 2 a, 2 c, and 2 e having the main cutting edges 6 at tip endsthereof so that a rotation trace a of the outer ends 11 of the cuttingblades 2 b, 2 d, and 2 f having the sub cutting edges 7 are locatedradially inward relative to a rotation trace b of the outer ends 12 ofthe cutting blades 2 a, 2 c, and 2 e having the main cutting edges 6.More specifically, in the case of a drill bit having an outer diameterin a range of approximately 6 mm to 20 mm, the outer ends 11 of the subcutting edges 7 are located radially inward relative to the outer ends12 of the main cutting edges 6 to have an appropriate distance betweenthe outer ends 11 and the outer ends 12 in a range of 0.2 mm to 0.5 mm.

Thus, the sub cutting edges 7 are shorter in length than the maincutting edges 6 since the positions of the inner ends and the positionsof the outer ends are different between the sub cutting edges 7 and themain cutting edges 6. Specifically, the sub cutting edges 7 may be about½ to ¼, particularly, about ⅓ to ¼ as long as the main cutting edges 6.The crush face 8 is located to retreat from the tip end 5 farther thanthe sub cutting edge 7. In this embodiment, a portion of the crush face8, which retreats farthest, is located to retreat substantially as faras the outer end 2 d of the sub cutting edges 7. A line 8 ccorresponding to an inner end of the crush face 8 extends in a directionsubstantially perpendicular to a line connecting the inner end 7 i ofthe sub cutting edge 7 to the center of the drill bit, to be precise, tocross the line at an angle of 85 degrees. Further, the crush face 8 isslightly inclined upward toward the flank 4 forming the sub cutting edge7. In this embodiment, the crush face 8 is inclined at an angle of about10 to 15 degrees. And, as seen from the tip end side (see FIGS. 2 and4), the crush face 8 is triangle shaped, substantiallyisosceles-triangle shaped (to be precise, deformed isosceles-triangleshaped because the sides cross each other at an angle of 85 degreesrather than 90 degrees).

As shown in FIG. 1, an angle (angle made by the main cutting edge 6 withrespect to the center line of the drill bit) a of the main cutting edge6 is equal to an angle β (angle made by the sub cutting edge 7 withrespect to the center line of the drill bit). In addition, as can beclearly shown in FIG. 1, the sub cutting edges 7 are located to retreatfrom the tip end 5 farther than the main cutting edges 6. The subcutting edges 7 may retreat relative to the main cutting edges 6 byabout 0.2 mm to 1.5 mm in the case of the drill bit having an outerdiameter of about 6 mm to 20 mm.

As shown in FIG. 1, as the drill bit is seen from the directionperpendicular to the longitudinal direction, the sub cutting edges 7 arerealized by retreating from the tip end 5 farther than the main cuttingedges 6 by reducing the thickness (dimension in a width direction) ofthe cutting blades 2 b, 2 d, and 2 f, that is, the sub cutting edges 7are parallel-shifted backward from the main cutting edges 6. But, thisstructure is not to be interpreted as limiting. For example, thisstructure may be realized by reducing a dimension of the edge betweenthe face 3 and the flank 4.

Concave portions substantially V-shape in cross section are each formedbetween the cutting blades 2 a and 2 b, 2 b and 2 c, 2 c and 2 d, 2 dand 2 e, 2 e and 2 f, and 2 f and 2 a and serve as chip dischargegrooves 9. These chip discharge grooves 9 communicate with bit chipdischarge grooves 10 provided on an outer periphery of the bit body 1.

Although not shown, a shank portion may be formed to extend from a baseportion of the bit body 1. The shank portion is held by a fixing meanssuch as chuck or the like attached to a drive shaft of a rotating hammerdrill. So, this drill bit can be replaced by a known commerciallyavailable drill bit during use.

The drill bit constructed as described above of the present invention isattached to the rotating hammer drill and functions as described belowin drilling the hole in concrete or the like.

In drilling a hole in the concrete, the stone, etc, cutting of thecutting face of the drill hole is done by the main cutting edges 6extending from the tip end 5 of the drill bit to the outer ends 12 ofthe cutting blade body 2. Small chips, which are included in chipscaused by cutting by the main cutting edges 6, move up from the cuttingface of the drill hole during repeated striking and cutting, and furthermove through the chip discharge grooves 9 each provided between thecutting blades 2 a, and 2 b, 2 b and 2 c, 2 c and 2 d, 2 d and 2 e, 2 eand 2 f, and 2 f and 2 a. These chips further move into the bit chipdischarge grooves 10 and are then smoothly discharged outside the drillhole.

Meanwhile, large chip lumps remaining around the center of the cuttingface of the drill hole is crushed by direct striking by the main cuttingedge 6 in subsequent striking and cutting, or otherwise enter a regionbetween the main cutting edges 6 and crushed into small chips by thecrush face 8 of the sub cutting edge 7. The crushed small chips arepushed into the chip discharge grooves 9 by the inclination of the crushface 8. And, large chip lumps remaining on the cutting face of the drillhole and being pushed toward a vicinity of an inner peripheral wall ofthe drill hole on the cutting face of the drill hole, are sandwichedbetween the main cutting edges 6 and crushed by striking by the subcutting edge 7 during striking and cutting. The crushed chips are pushedout into the chip discharge grooves 9 by the inclination of the cuttingfaces 8. As should be appreciated, the large chip lumps generated on thecutting face of the drill bit are efficiently crushed by cooperationbetween the main cutting edges 6 and the sub cutting edges 7. As aconsequence, drilling is accomplished with high drilling efficiency.

During drilling, a cutting force is always applied by the cooperationbetween the main cutting edges 6 and the sub cutting edges 7 whichdiffer in length and placement from each other and differs in distancefrom the tip end 5. So, the cooperation stably continues without beingsubstantially affected by a great change in a drilling condition due tostriking of the cutting edges on the reinforcing steel within theconcrete, the stone, etc

INDUSTRIAL APPLICABILITY

In accordance with the drill bit constructed as described above,regardless of a great change in a drilling condition due to striking ofa tip end of the drill bit against concrete, stone, etc, drilling can becarried out as stably as possible by lessening the change. In addition,since large chip lumps can be effectively crushed by cooperation betweenmain cutting edges and sub cutting edges without impeding striking andcutting, drilling is carried out without reducing drilling efficiency.

1. A drill bit comprising: a plurality of cutting blades disposed at atip end of a drill, each of the cutting blades extending substantiallyradially outward from a rotation center side of the drill, each of thecutting blades having a cutting edge formed by protruding an edgebetween a face and a flank of each cutting blade toward a tip end of thedrill, and a shaft-shaped bit body attached to a base end side of thecutting blades and having a base end portion coupled to a shank portion,the drill bit being configured to perform striking and cutting by acombination of a rotation and an axial movement, wherein the cuttingblades include main cutting blades and sub cutting blades, the maincutting blades including radially oriented main cutting edges, each ofthe main cutting edges extending radially to an inner end and convergingat a rotational and geometric center of the drill bit to form a pointedtip end, each of the main cutting blades having an outer end located onan outer periphery of a rotation trace of the drill bit; the sub cuttingblades including exclusively linear sub cutting edges extending in theradial direction, each of the sub cutting edges having an inner endspaced radially outward apart from the rotational and geometric centerand an outer end spaced radially inward from the outer periphery of therotation trace, and a planar crush face formed between the inner end ofeach sub cutting edge and the rotational and geometric center to retreatfrom the sub cutting edge such that the crush face is inclined downwardon the flank side of the sub cutting blade, an outer extent of eachcrush face terminating at the inner end of the adjacent sub cuttingblade.
 2. The drill bit of claim 1 wherein each crush face is atriangle.